He was born into a Quaker family and thus he had a duty to run a profitable but also very fair business. He joined his brother in 1869 and by 1875 Joseph as describing "himself as a cocoa manufacturer". (2)
Joseph continued in this firm until 1923 when he finally retired leaving behind a legacy of cocoa and chocolate products as well as a community focus that was common to Quaker chocolatiers of this period. Today three trust funds carry out his charitable work and another has been added later in the company's life.
Rowntree continued to make chocolate throughout the 20th century and merged with Mackintosh's in 1969. By 1988 it was acquired by Nestlé after a contentious fight with another company. Only a few products today are manufactured using the Rowntree name. Just like the Vanhouten cocoas, these products are primarily available in Europe, but especially in the UK. I hope some of our UK readers let us know if they've had any Rowntree chocolate items.
1: Image from JRHT
2: Information from the Rowntree Society